title: Nitric oxide short-circuits interleukin-12-mediated tumor regression.
abstract: Interleukin-12 (IL-12) can promote tumor regression via activation of multiple lymphocytic and myelocytic effectors. Whereas the cytotoxic mechanisms employed by T/NK/NKT cells in IL-12-mediated tumor kill are well defined, the antitumor role of macrophage-produced cytotoxic metabolites has been more controversial. To this end, we investigated the specific role of nitric oxide (NO), a major macrophage effector molecule, in post-IL-12 tumor regression. Analysis of tumors following a single intratumoral injection of slow-release IL-12 microspheres showed an IFNγ-dependent sevenfold increase in inducible nitric oxide synthase (iNOS) expression within 48 h. Flow cytometric analysis of tumor-resident leukocytes and in vivo depletion studies identified CD11b(+) F4/80(+) Gr1(lo) macrophages as the primary source of iNOS. Blocking of post-therapy iNOS activity with N-nitro-L: -arginine methyl ester (L-NAME) dramatically enhanced tumor suppression revealing the inhibitory effect of NO on IL-12-driven antitumor immunity. Superior tumor regression in mice receiving combination treatment was associated with enhanced survival and proliferation of activated tumor-resident CD8+ T-effector/memory cells (Tem). These findings demonstrate that macrophage-produced NO negatively regulates the antitumor activity of IL-12 via its detrimental effects on CD8+ T cells and identify L-NAME as a potent adjuvant in IL-12 therapy of cancer.
authors.affiliation: Department of Microbiology and Immunology, School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY 14214, USA. negilmez@buffalo.edu
authors.forename: Nejat K
authors.initials: NK
authors.lastname: Egilmez
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Harden
authors.forename: Lauren P
authors.initials: LP
authors.lastname: Virtuoso
authors.forename: Reto A
authors.initials: RA
authors.lastname: Schwendener
authors.forename: Mehmet O
authors.initials: MO
authors.lastname: Kilinc
mesh_terms: D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology* / Q000473:pathology; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D015552:Injections, Intralesional; D018664:Interleukin-12 / Q000037:antagonists & inhibitors / Q000276:immunology* / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000187:drug effects; D016246:Lymphocytes, Tumor-Infiltrating / Q000187:drug effects / Q000276:immunology; D008264:Macrophages / Q000187:drug effects / Q000201:enzymology / Q000276:immunology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000276:immunology* / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000276:immunology / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D012333:RNA, Messenger; D018664:Interleukin-12; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II; D019331:NG-Nitroarginine Methyl Ester